Certain advanced color printers contain inline spectrophotometers for use in color matching. Color matching is the process of ensuring that a newly printed or otherwise applied color appears the same as a desired color. In printing, color matching is critical in many applications such as photographic printing and branding. Photographic printing covers such applications as printing photographs in magazines, brochures, and advertising materials. Branding often requires the precise reproduction of certain specific colors that are associated with a brand such as a corporate logo or other trademark/service mark. Specific colors that must be reproduced precisely are known as spot colors.
The spot colors are often available in the form of a swatch or other color reference that can be measured by an offline spectrophotometer to produce a measurement in the L*, a*, b* color space. As is well known in the printing arts, colors are often defined in L*, a*, b* coordinates because the color definition is thereby “device independent”. The device independent color definitions are converted into device dependent color specifications before printing. A printed spot color rarely exactly matches the color reference for a variety of reasons. The difference between the printed spot color and the reference color is often called a color matching error.
One source of matching errors is that different printers, even those using the same inks, usually produce slightly different colors when given the same device dependent color specifications. As such, the conversions themselves are often device dependent when mapping device independent color definitions to device dependent color specifications. Some details of color space conversion and color gamut mapping are detailed in U.S. Patent Applications 2008/0043271 and 2008/0043264 which are both herein included by reference. These patent applications also detail the operation of certain automated spot color editors (ASCEs).
The terms “device dependent color specification” and “device independent color definition” are used throughout this document. In keeping with convention, these terms refer to dependence or independence on the marking device, not on the color measurement instrument. Thus a “device dependent color specification” would be, for example, in CMYK colorant space, while a “device independent color definition” would be, for example, in L*, a*, b* color space. While L*, a*, b* color measurements do certainly depend to some extent on the instrument on which they are measured, and such dependence is in fact an important aspect of this invention, this is not at all meant by the term “device dependent”.
Current techniques for matching spot colors work well but still produce measurable matching errors. Systems and methods that further reduce or eliminate those measurable matching errors are needed.